The invention relates to a shaft supporting mechanism for a mixing and kneading device in which a mixing and kneading blade is releasably arranged. In particular, the invention is directed to a shaft supporting mechanism for a mixing and kneading device of a domestically used bread making machine that bakes bread after preparing dough while pouring bread making ingredients into a bread baking case and mixing and kneading the ingredients therein, and then fermenting the prepared dough.
A conventional bread making machine for home use is usually designed so that ingredients such as flour, water, and yeast are poured into a bread baking case arranged inside a closed container; dough is prepared by mixing and kneading the ingredients in the case; the dough is subjected to first fermentation and second fermentation; and the fermented dough is finally baked. The mixing and kneading operation is performed by stirring the bread making ingredients such as flour, water, and yeast with a mixing and kneading blade provided on the bottom of the bread baking case.
The shaft supporting mechanism for the mixing and kneading device in such a conventional bread making machine or the like will be described below.
The conventional shaft supporting mechanism for the mixing and kneading device is constructed of a D cut shaft, which is a rotating shaft. The mixing and kneading blade having an insertion hole is inserted into the D cut shaft. FIG. 8 is a perspective view of such a rotating shaft.
In FIG. 8, the rotating shaft is shown as a D cut shaft 30 whose diameter is d1. The D cut is formed by cutting a part of a circumferential portion at an end portion of a round rod-like shaft. An axially extending D cut plane surface 30a is provided. The section of a shaft portion on which the D cut is arranged is therefore D-shaped with a part thereof arcuately removed. Here, reference character 30m designates the upper end surface of the D cut shaft 30.
FIG. 5 is a side view of the mixing and kneading blade that is to be inserted into the D cut shaft 30; FIG. 6 is a diagram as viewed from A in FIG. 5 (a top view); and FIG. 7 is a diagram as viewed from B of FIG. 5.
In FIGS. 5 to 7, a mixing and kneading blade 14 is formed of a shaft portion 14a and a blade portion integrally with a synthetic resin, the blade radially extending from the shaft portion 14a. The blade 14 rotates in an .alpha. direction around the shaft portion 14a. The blade portion, having inclined surfaces 14d and 14e, is formed into plate-like sloped surfaces so that the bread making ingredients can be pushed up frontward in the .alpha. direction. The inclined surface 14d has a large inclination as shown in FIG. 7.
The shaft portion 14a has an axially extending insertion hole 14b. The insertion hole 14b has a diameter d2, which is a value slightly larger than the diameter d1 of the D cut shaft 30. The section of the insertion hole 14b is a circle with a part thereof arcuately removed. It is a plane abutment surface 14c, that is equivalent to a chord subtending the arcuately removed portion.
The D cut shaft 30 is inserted into the insertion hole 14b of the mixing and kneading blade 14 so as to mesh the D cut surface 30a with the abutment surface 14c. With the diameter d2 of the insertion hole 14b being slightly larger than the diameter d1 of the D cut shaft 30, the mixing and kneading blade 14 is releasable from the shaft 30. This arrangement allows the mixing and kneading blade 14 to be taken out together and simultaneously with the dough or the bread after the mixing and kneading process or after the whole bread making process so that the dough or the bread will not be damaged.
FIG. 9 shows, through a two-dotted chain line, the section of the insertion hole 14b of the mixing and kneading blade 14, the section being taken along the upper end surface 30m of the D cut shaft 30 immediately before rotation. Since the insertion hole 14b is slightly larger than the outer diameter of the D cut shaft 30, a gap 31 is provided between these components as shown in FIG. 9 immediately before the rotation of the shaft.
Then, when the D cut shaft 30 is rotated in the .alpha. direction by the rotating means coupled to the D cut shaft 30, a point M on the upper end surface 30m of the D cut shaft 30 abuts against the abutment surface 14c of the mixing and kneading blade 14 as schematically shown in FIG. 9, thereby biasing the abutment surface 14c. As a result of the abutment surface 14c having been biased, the mixing and kneading blade 14 is rotated in the .alpha. direction.
When the thus constructed mixing and kneading blade 14 is rotated on the bottom of the bread baking case, the poured bread making ingredients come in contact with the inclined surfaces 14d and 14e in rotation. Since the inclined surfaces 14d and 14e are inclined, the bread making ingredients are pushed upward while coming in contact with the inclined surfaces. As a result of this operation, the bread making ingredients are mixed and stirred with respect to the bread baking base, and this contributes to uniformly mixing and kneading the bread making ingredients.
By the way, when the viscosity of the bread making ingredients is increased with the gluten in the flour becoming sticky while the mixing and kneading process is being progressed, the bread making ingredients come to make a complicated motion. Thus, the mixing and kneading blade 14 may, in some cases, be released from the D cut shaft 30. For example, the volume of the bread making ingredients under the inclined surfaces 14d and 14e is increased, so that a force for pushing up the inclined surfaces 14d and 14e is easily generated. If such an upwardly pushing force is produced, the insertion hole 14b of the mixing and kneading blade 14 is pushed up to the upper part of the D cut shaft 30, not only making the mixing and kneading operation unstable but also making it likely to release the mixing and kneading blade 14 from the D cut shaft 30 in an extreme case.
Since the diameter d2 of the insertion hole 14b is slightly larger than the diameter d1 of the D cut shaft 30 for the aforementioned reason, the mixing and kneading blade 14 is quite likely to come off the D cut shaft 30 in the conventional example, which has been a problem.